This invention relates in general to a luminous gas discharge display and in particular to a luminous display such as a sign employing a gas discharge and a method of manufacturing such a display.
Luminous signs employing a gaseous discharge and methods for making such signs have been disclosed in several patents. In general, these signs are made by using two or three glass plates with a groove or cavity corresponding to the desired display formed in one or two of the plates. When three plates are used, the groove or cavity can be formed in the intermediate plate which is disposed between a pair of outer plates. Alternately, the intermediate plate can be omitted with the groove or cavity formed in an interior surface of one or both of the outer plates. The cavity is hermetically sealed and communicates with a set of electrodes. In the manufacturing process, the cavity is evacuated and a quantity of ionizable gas, such as neon, is introduced into the cavity through a gas charging port. The gas is then ionized by applying a voltage across the electrode set. The ionized gas, in turn, causes the display to illuminate.
This invention relates to a luminous gas display and a method of manufacturing such a display.
As described above, it is known to evacuate the space between the plates of a luminous gas display. As described above, in an effort to reduce the thickness of such displays, it is known to omit the intermediate plate and form the display channels in the interior surface of one or both of the outer plates. The channels are shaped to conform to the desired symbols. Alternately, ridges can be formed in the surface of one of the plates. A sealant is applied about the perimeter of one of the plates and the plates are assembled. By making one, or both, of the plates sufficiently thin, atmospheric pressure will urge the center of the plates toward one another as the space therebetween is evacuated, causing one or both of the plates to be slightly bowed. As the edges of the channels or the crest of the ridges contact the bowed plate surface, a channel for containing the ionizable gas is formed. The channel is then charged with the ionizable gas.
To further enhance the display, it is also known to apply a light emitting phosphor coating to the channel. A small quantity of Mercury (Hg) is introduced into the channel. When the gas in the channel is ionized, the Hg is heated and vaporizes. The Hg vapor produces Ultra-Violet (UV) radiation which excites the phosphor to produce a brighter and/or more colorful display. Additionally, use of different phosphors can provide a variety of colors for the display.
If a seal is not formed along the entire length of the channel, the Hg vapor may leak into the evacuated portion of the display. Because Hg vapor is a condensing gas, when the Hg vapor contacts the cold portions of the display panels, the Hg vapor reverts to its liquid state and condenses upon the interior surface of the panels. Once out of the channel, the Hg is not heated by the ionized gas and thus will remain in its liquid state. The loss of Hg vapor from the channel can cause weak illumination of portions of the display. Eventually, all of the Hg vapor may escape from the channel and condense upon the panels, removing the source of UV radiation for exciting the phosphor coating in the channel. Accordingly, it would be desirable to provide a luminous gas display which includes a seal formed along the edge of the gas charged channel which would prevent the Hg vapor from escaping from the channel.
The present invention contemplates a luminous gas discharge display including a first plate and a second plate adjacent to the first plate. The display further includes a layer of sealing material disposed between the plates and forming a seal therebetween. At least one channel is formed in an interior surface of at least one of the first and second plates. The channel contains an ionizable gas and a pair of electrodes communicate with the channel. The electrodes are operable to ionize the gas in the channel to produce a gas discharge display.
The invention further contemplates that at least one of the first and second plates is transparent and further that the sealing layer also is transparent. In the preferred embodiment, the plates are formed from glass and the dielectric layer is formed from a sealing glass compound, such as solder glass. Additionally, the thermal coefficient of expansion for the sealing layer is approximately the same as the thermal coefficient of expansion for both of the display plates. The sealing layer can extend across the entire interior surface of at least one of the plates or the sealing material can be deposited upon the plate which includes the channel with a band of the sealing material adjacent to the perimeter of the channel.
The present invention also contemplates a process for fabricating a luminous gas discharge display which includes forming at least two plates. At least one channel is formed in one of the plates. A layer of light emitting phosphor is deposited in the channel and a layer of sealing material is applied to at least one of the plates and cured thereon. The plates are then assembled with the channel and the layer of sealing material between the plates to form a plate assembly. The plate assembly is heated to a joining temperature, which is a function of the sealing material and the glass forming the plates, and maintained at the temperature for a period of time sufficiently long to cause the dielectric material to join the plates together and form a seal therebetween. A source of liquid mercury can be deposited in the channel. The channel is then evacuated and refilled with an ionizable gas. The channel is then sealed and the mercury is activated. In the preferred embodiment, an ampule of mercury is placed in the channel and the mercury activated by being released from the ampule once the channel is sealed. Either a pair of internal electrodes which communicate with the channel are installed before the plates are assembled, or a pair of external electrodes which communicate with the channel are installed after the plate assembly is joined.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.